This drive device (100) drives an electric motor (1) having a coil (3). The drive device (100) is provided with a converter (102) which generates a bus voltage, an inverter (103) which converts the bus voltage to an AC voltage and supplies this to the coil (3), and a connection switching unit (60) which switches the connection state of the coil (3). The bus voltage generated by the converter (102) is switched depending on the connection state of the coil (3).